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Ticks carry decades of history in each troublesome bite

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theconversation.com – Sean Lawrence, Assistant Professor of History, West Virginia University – 2025-06-18 07:45:00


Ticks are the most common disease-carrying parasites in the U.S., spreading illnesses like Lyme disease, babesiosis, and Rocky Mountain spotted fever. Human actions—like 18th- and 19th-century deforestation in the Northeast—led to regrowth of forests without predators, causing deer and tick populations to surge. In California, urban sprawl fragments habitats, increasing tick infection rates. Historical livestock management in Texas curbed cattle fever by controlling tick movement. Globally, shifts in land use, such as Ottoman Empire policies forcing nomads to settle, expanded tick habitats and disease spread. Ultimately, ticks thrive due to environmental changes largely driven by human activity.

The black-legged tick, or deer tick, Ixodes scapularis, can transmit Lyme disease and other health hazards.
U.S. Centers for Disease Control and Prevention

Sean Lawrence, West Virginia University

When you think about ticks, you might picture nightmarish little parasites, stalking you on weekend hikes or afternoons in the park.

Your fear is well-founded. Tick-borne diseases are the most prevalent vector-borne diseases – those transmitted by living organisms – in the United States. Each tick feeds on multiple animals throughout its life, absorbing viruses and bacteria along the way and passing them on with its next bite. Some of those viruses and bacteria are harmful to humans, causing diseases that can be debilitating and sometimes lethal without treatment, such as Lyme, babesiosis and Rocky Mountain spotted fever.

But contained in every bite of this infuriating, insatiable pest is also a trove of social, environmental and epidemiological history.

In many cases, human actions long ago are the reason ticks carry these diseases so widely today. And that’s what makes ticks fascinating for environmental historians like me.

Two small ticks on a person' index finger. The nymph could pass for a freckle.
Ticks can be tiny and hard to spot. This is an adult and nymph Ixodes scapularis on an adult’s index finger.
CDC

Changing forests fueled tick risks

During the 18th and 19th centuries, settlers cleared more than half the forested land across the northeastern U.S., cutting down forests for timber and to make way for farms, towns and mining operations. With large-scale land clearing came a sharp decline in wildlife of all kinds. Predators such as bears and wolves were driven out, as were deer.

As farming moved westward, Northeasterners began to recognize the ecological and economic value of trees, and they returned millions of acres to forest.

The woods regrew. Plant-eaters such as deer returned, but the apex predators that once kept their populations in check did not.

As a result, deer populations grew rapidly. With the deer came deer ticks (Ixodes scapularis) carrying borrelia burgdorferi, the bacterium that causes Lyme disease. When a tick feeds on an infected animal, it can take up the bacteria. The tick can pass the bacteria to its next victim. In humans, Lyme disease can cause fever and fatigue, and if left untreated it can affect the nervous system.

The eastern U.S. became a global hot spot for tick-borne Lyme disease starting around the 1970s. Lyme disease affected over 89,000 Americans in 2023, and possibly many more.

Californians move into tick territory

For centuries, changing patterns of human settlements and the politics of land use have shaped the role of ticks and tick-borne illnesses within their environments.

In short, humans have made it easier for ticks to thrive and spread disease in our midst.

In California, the Northern Inner Coast and Santa Cruz mountain ranges that converge on San Francisco from the north and south were never clear-cut, and predators such as mountain lions and coyotes still exist there. But competition for housing has pushed human settlement deeper into wildland areas to the north, south and east of the city, reshaping tick ecology there.

A range map for the western black-legged tick.
National Center for Emerging and Zoonotic Infectious Diseases

While western black-legged ticks (Ixodes pacificus) tend to swarm in large forest preserves, the Lyme-causing bacterium is actually more prevalent in small, isolated patches of greenery. In these isolated patches, rodents and other tick hosts can thrive, safe from large predators, which need more habitat to move freely. But isolation and lower diversity also means infections are spread more easily within the tick’s host populations.

People tend to build isolated houses in the hills, rather than large, connected developments. As the Silicon Valley area south of San Francisco sprawls outward, this checkerboard pattern of settlement has fragmented the natural landscape, creating a hard-to-manage public health threat.

Fewer hosts, more tightly packed, often means more infected hosts, proportionally, and thus more dangerous ticks.

A magnified view of a tick's mouth.
A tick’s mouth is barbed so it can hold on as it draws blood over hours.
National Institute of Allergy and Infectious Diseases

Six counties across these ranges, all surrounding and including San Francisco, account for 44% of recorded tick-borne illnesses in California.

A lesson from Texas cattle ranches

Domesticated livestock have also shaped the disease threat posed by ticks.

In 1892, at a meeting of cattle ranchers at the Stock Raiser’s Convention in Austin, Texas, Dr. B.A. Rogers introduced a novel theory that ticks were behind recent devastating plagues of Texas cattle fever. The disease had arrived with cattle imported from the West Indies and Mexico in the 1600s, and it was taking huge tolls on cattle herds. But how the disease spread to new victims had been a mystery.

A detailed illustration of a tick, drawn at the time people were debating the tick's role in cattle fever.
A 1905 illustration of Rhipicephalus annulatus, a hard tick that causes cattle fever.
Nathan Banks, A treatise on the Acarina, or mites. Proceedings of the United States National Museum

Editors of Daniel’s Texas Medical Journal found the idea of ticks spreading disease laughable and lampooned the hypothesis, publishing a satire of what they described as an “early copy” of a forthcoming report on the subject.

The tick’s “fluid secretion, it is believed, is the poison which causes the fever … [and the tick] having been known to chew tobacco, as all other Texans do, the secretion is most probably tobacco juice,” they wrote.

Fortunately for the ranchers, not to mention the cows, the U.S. Department of Agriculture sided with Rogers. Its cattle fever tick program, started in 1906, curbed cattle fever outbreaks by limiting where and when cattle should cross tick-dense areas.

A person holds open a calf's ear to show several engorged ticks.
Engorged ticks feed on a calf’s ear.
Alan R Walker, CC BY-NC-SA

By 1938, the government had established a quarantine zone that extended 580 miles by 10 miles along the U.S.-Mexico border in South Texas Brush Country, a region favored by the cattle tick.

This innovative use of natural space as a public health tool helped to functionally eradicate cattle fever from 14 Southern states by 1943.

Ticks are products of their environment

When it comes to tick-borne diseases the world over, location matters.

Take the hunter tick (Hyalomma spp.) of the Mediterranean and Asia. As a juvenile, or nymph, these ticks feed on small forest animals such as mice, hares and voles, but as an adult they prefer domesticated livestock.

For centuries, this tick was an occasional nuisance to nomadic shepherds of the Middle East. But in the 1850s, the Ottoman Empire passed laws to force nomadic tribes to become settled farmers instead. Unclaimed lands, especially on the forested edges of the steppe, were offered to settlers, creating ideal conditions for hunter ticks.

As a result, farmers in what today is Turkey saw spikes in tick-borne diseases, including a virus that causes Crimean-Congo hemorrhagic fever, a potentially fatal condition.

Where to check for ticks and how to remove them.

It’s probably too much to ask for sympathy for any ticks you meet this summer. They are bloodsucking parasites, after all.

Still, it’s worth remembering that the tick’s malevolence isn’t its own fault. Ticks are products of their environment, and humans have played many roles in turning them into the harmful parasites that seek us out today.

This article has been updated to clarify that ticks spread alongside the deer population.The Conversation

Sean Lawrence, Assistant Professor of History, West Virginia University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Political Bias Rating: Centrist

This content provides a fact-based, historical, and scientific overview of tick-borne diseases and their environmental context without promoting a specific political ideology. It discusses human impacts on ecology and public health in a neutral tone, focusing on empirical evidence and historical examples rather than partisan viewpoints. The article emphasizes the complex interactions between humans, environment, and disease, reflecting an objective approach typical of centrist or nonpartisan informational sources.

The Conversation

How artificial intelligence controls your health insurance coverage

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theconversation.com – Jennifer D. Oliva, Professor of Law, Indiana University – 2025-06-20 07:25:00


Over the past decade, health insurers have increasingly used AI algorithms to decide whether to approve and pay for medical treatments recommended by doctors. These algorithms often determine if care is “medically necessary,” influencing coverage and treatment duration. While insurers claim AI speeds decisions and cuts waste, evidence shows it can delay or deny needed care, disproportionately affecting chronically ill and minority patients. These algorithms remain largely secret and unregulated, raising concerns about fairness and safety. Although some states and CMS have introduced rules, experts argue FDA oversight or federal regulation is needed to ensure transparency, accuracy, and patient protection.

Evidence suggests that insurance companies use AI to delay or limit health care that patients need.
FatCameraE+ via Getty Images

Jennifer D. Oliva, Indiana University

Over the past decade, health insurance companies have increasingly embraced the use of artificial intelligence algorithms. Unlike doctors and hospitals, which use AI to help diagnose and treat patients, health insurers use these algorithms to decide whether to pay for health care treatments and services that are recommended by a given patient’s physicians.

One of the most common examples is prior authorization, which is when your doctor needs to
receive payment approval from your insurance company before providing you care. Many insurers use an algorithm to decide whether the requested care is “medically necessary” and should be covered.

These AI systems also help insurers decide how much care a patient is entitled to — for example, how many days of hospital care a patient can receive after surgery.

If an insurer declines to pay for a treatment your doctor recommends, you usually have three options. You can try to appeal the decision, but that process can take a lot of time, money and expert help. Only 1 in 500 claim denials are appealed. You can agree to a different treatment that your insurer will cover. Or you can pay for the recommended treatment yourself, which is often not realistic because of high health care costs.

As a legal scholar who studies health law and policy, I’m concerned about how insurance algorithms affect people’s health. Like with AI algorithms used by doctors and hospitals, these tools can potentially improve care and reduce costs. Insurers say that AI helps them make quick, safe decisions about what care is necessary and avoids wasteful or harmful treatments.

But there’s strong evidence that the opposite can be true. These systems are sometimes used to delay or deny care that should be covered, all in the name of saving money.

A pattern of withholding care

Presumably, companies feed a patient’s health care records and other relevant information into health care coverage algorithms and compare that information with current medical standards of care to decide whether to cover the patient’s claim. However, insurers have refused to disclose how these algorithms work in making such decisions, so it is impossible to say exactly how they operate in practice.

Using AI to review coverage saves insurers time and resources, especially because it means fewer medical professionals are needed to review each case. But the financial benefit to insurers doesn’t stop there. If an AI system quickly denies a valid claim, and the patient appeals, that appeal process can take years. If the patient is seriously ill and expected to die soon, the insurance company might save money simply by dragging out the process in the hope that the patient dies before the case is resolved.

Insurers say that if they decline to cover a medical intervention, patients can pay for it out of pocket.

This creates the disturbing possibility that insurers might use algorithms to withhold care for expensive, long-term or terminal health problems , such as chronic or other debilitating disabilities. One reporter put it bluntly: “Many older adults who spent their lives paying into Medicare now face amputation or cancer and are forced to either pay for care themselves or go without.”

Research supports this concern – patients with chronic illnesses are more likely to be denied coverage and suffer as a result. In addition, Black and Hispanic people and those of other nonwhite ethnicities, as well as people who identify as lesbian, gay, bisexual or transgender, are more likely to experience claims denials. Some evidence also suggests that prior authorization may increase rather than decrease health care system costs.

Insurers argue that patients can always pay for any treatment themselves, so they’re not really being denied care. But this argument ignores reality. These decisions have serious health consequences, especially when people can’t afford the care they need.

Moving toward regulation

Unlike medical algorithms, insurance AI tools are largely unregulated. They don’t have to go through Food and Drug Administration review, and insurance companies often say their algorithms are trade secrets.

That means there’s no public information about how these tools make decisions, and there’s no outside testing to see whether they’re safe, fair or effective. No peer-reviewed studies exist to show how well they actually work in the real world.

There does seem to be some momentum for change. The Centers for Medicare & Medicaid Services, or CMS, which is the federal agency in charge of Medicare and Medicaid, recently announced that insurers in Medicare Advantage plans must base decisions on the needs of individual patients – not just on generic criteria. But these rules still let insurers create their own decision-making standards, and they still don’t require any outside testing to prove their systems work before using them. Plus, federal rules can only regulate federal public health programs like Medicare. They do not apply to private insurers who do not provide federal health program coverage.

Some states, including Colorado, Georgia, Florida, Maine and Texas, have proposed laws to rein in insurance AI. A few have passed new laws, including a 2024 California statute that requires a licensed physician to supervise the use of insurance coverage algorithms.

But most state laws suffer from the same weaknesses as the new CMS rule. They leave too much control in the hands of insurers to decide how to define “medical necessity” and in what contexts to use algorithms for coverage decisions. They also don’t require those algorithms to be reviewed by neutral experts before use. And even strong state laws wouldn’t be enough, because states generally can’t regulate Medicare or insurers that operate outside their borders.

A role for the FDA

In the view of many health law experts, the gap between insurers’ actions and patient needs has become so wide that regulating health care coverage algorithms is now imperative. As I argue in an essay to be published in the Indiana Law Journal, the FDA is well positioned to do so.

The FDA is staffed with medical experts who have the capability to evaluate insurance algorithms before they are used to make coverage decisions. The agency already reviews many medical AI tools for safety and effectiveness. FDA oversight would also provide a uniform, national regulatory scheme instead of a patchwork of rules across the country.

Some people argue that the FDA’s power here is limited. For the purposes of FDA regulation, a medical device is defined as an instrument “intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease.” Because health insurance algorithms are not used to diagnose, treat or prevent disease, Congress may need to amend the definition of a medical device before the FDA can regulate those algorithms.

If the FDA’s current authority isn’t enough to cover insurance algorithms, Congress could change the law to give it that power. Meanwhile, CMS and state governments could require independent testing of these algorithms for safety, accuracy and fairness. That might also push insurers to support a single national standard – like FDA regulation – instead of facing a patchwork of rules across the country.

The move toward regulating how health insurers use AI in determining coverage has clearly begun, but it is still awaiting a robust push. Patients’ lives are literally on the line.The Conversation

Jennifer D. Oliva, Professor of Law, Indiana University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Note: The following A.I. based commentary is not part of the original article, reproduced above, but is offered in the hopes that it will promote greater media literacy and critical thinking, by making any potential bias more visible to the reader –Staff Editor.

Political Bias Rating: Center-Left

This content takes a critical stance on health insurance companies’ use of AI algorithms, emphasizing concerns about transparency, fairness, and potential harm to vulnerable populations. The critique aligns with progressive views favoring stronger regulatory oversight, consumer protection, and addressing systemic inequities in healthcare. However, the article remains measured, acknowledging insurers’ stated benefits and existing regulatory actions, which positions it left-leaning but not radically so. The focus on government intervention and protection of marginalized groups typically resonates with center-left perspectives on social justice and market regulation.

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How to stay safe during heat waves – and the heat stroke warning signs to watch for

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theconversation.com – Brian Bossak, Professor of Public Health, College of Charleston – 2025-06-19 13:57:00


As the first major U.S. heat wave of 2025 arrives, experts warn of rising health risks, especially for outdoor workers, older adults, and those without air conditioning. Heat-related illnesses range from mild cramps to life-threatening heat stroke, which can rapidly damage organs if untreated. Warning signs include dizziness, nausea, and halted sweating. The heat index, influenced by humidity, better gauges danger than temperature alone. Staying safe includes hydrating with electrolytes, resting in cool environments, and avoiding strenuous activity during peak heat. Fans aren’t always safe, especially above 95°F. Communities should support vulnerable populations with access to cooling centers and wellness checks.

Extreme heat can become lethal quickly. A young man cools off at Washington, D.C.’s Yards Park during a heat wave in 2021.
Olivier Douliery/AFP via Getty Images

Brian Bossak, College of Charleston

Beach trips, cookouts and other outdoor activities are in full swing as summer arrives and the first widespread heat wave of 2025 hits the U.S.

For many people, summer is their favorite time of year. However, summer also brings the risk of dangerously high temperatures.

In the U.S., hundreds of people working or playing outside – even those who seem healthy – succumb to heat-related illnesses each year. Older adults and people in areas that historically haven’t needed air conditioning tend to see the highest rates of illnesses during heat waves, as Chicago saw in 1995 when at least 700 people died in a heat wave.

Even in places where heat is recognized as a dangerous health threat, people can be caught off guard as the thermometer creeps higher, on average, each year. In some cases, dangerous heat can arise quickly. In 2021, a young family died of heat stroke on a California trail after setting out for a hike when temperatures were still in the 70s Fahrenheit (low to mid 20s Celsius).

I study health risks in a warming climate as a professor of public health, and I’ve seen heat become a growing concern. Here are some of the key warning signs to watch for when temperatures rise – and ways to keep cool when the heat and humidity get too high.

Signs of heat-related illness to watch for

Heat-related illnesses occur across a spectrum, and mild heat stress can quickly progress to life-threatening heat stroke if a person is exposed to dangerous conditions for too long.

Mild forms of heat-related illness include heat cramps and heat rash, both of which can be caused by extensive sweating during hot conditions. Cooling the body and drinking cool fluids can help.

When heat-related illnesses progress into heat exhaustion, the situation is more serious. Heat exhaustion includes symptoms such as dizziness, nausea, excessive sweating, feeling weak, thirst and getting a headache.

A construction worker sits and puts his head down, still in the hot sun.
Construction workers are often out in the heat for long periods of time while wearing long sleeves, durable long pants, gloves and hard hats considered necessary to stay safe. This worker faces a heat wave in Los Angeles in July 2024.
Etienne Laurent/AFP via Getty Images

Heat exhaustion is a signal that the body is losing its ability to maintain a stable core temperature. Immediate action such as moving to a cool, ideally air-conditioned space, drinking liquids, loosening clothes and applying wet cloths are some of the recommended steps that can help keep heat exhaustion from progressing to the most dangerous form of heat-related illness, heat stroke.

Heat stroke is a medical emergency. At this point, the body can no longer maintain a stable core temperature. A body with heat stroke can reach 106 degrees Fahrenheit or higher rapidly, and that heat can quickly damage the brain, heart and kidneys.

An illustration showing symptoms associated with heat exhaustion, such as dizziness, heavy sweating, nausea and weakness; and with heat stroke, including confusion, dizziness and passing out.
Signs of heat exhaustion and heat stroke, from the National Weather Service and Centers for Disease Control and Prevention.
NOAA/CDC

Typically, someone suffering heat stroke has exhausted their reserves of sweat and salt to stay cool, so sweating eventually stops during heat stroke. Their cognitive ability fails, and they cannot remove themselves from danger. Heat stroke can cause seizures or put someone into a coma as their core temperature rises. If the condition is not treated immediately, and the core temperature continues to rise, heat stroke becomes fatal.

Because heat exhaustion can lead to heat stroke, addressing heat-related illnesses before they progress is vital.

How to tell when the heat is too high

Heat risk isn’t just about temperature – humidity also increases the risk of heat-related illnesses because it affects how well sweating will cool the human body when it gets hot.

Instead of just looking at temperature when planning outdoor activities, check the heat index, which accounts for heat illness risk associated with temperature and relative humidity.

It doesn’t take very high temperatures or very high humidity for the heat index to enter dangerous territory.

A chart shows how humidity and temperature combine for dangerous conditions. For example, 86 degrees F at 80% humidity is a heat index of 100. 94 degrees at 45% humidity is also a heat index of 100.
A heat index chart shows how heat and humidity combine for dangerous conditions.
NOAA

However, the heat index is still a conservative measure of the impact of heat on humans, particularly for outdoor workers and athletes at summer practices. This is because temperature measurements used in weather forecasting are taken in the shade and are not exposed to direct sunlight. If someone is outside and exposed to the direct sun, the actual heat index can be as much as 15 F higher than the heat index chart indicates.

A more sophisticated measurement of heat effects on human health is what’s known as the wet-bulb globe temperature, which takes into account other variables, such as wind speed and cloud cover. Neither takes into account a person’s physical exertion, which also raises their body temperature, whether working at a construction site or playing soccer.

Tips for staying safe in a heat wave

How can you stay cool when heat waves set in? The answer depends in part on where you are, but the main points are the same:

  • Avoid strenuous outdoor activities in high temperatures if possible. If you start to feel symptoms of heat-related illnesses, drink fluids that will hydrate you. Find shade, rest, and use cool, damp cloths to lower your body temperature. If you see signs of heat stroke in someone else, call for medical help.

  • Be careful with fans. Fans can be useful if the temperature isn’t too high because they wick sweat away from the body and induce evaporative cooling. But at very high temperatures, they can accelerate heat buildup in the body and lead to dangerous conditions. If indoor temperatures reaches 95 degrees or higher, using fans can actually be dangerous and raise the risk of heat-related illnesses.

  • Find a cooling center, library or community center where you can get inside and rest in an air-conditioned space in the hottest hours. In places such as Phoenix, where high temperatures are a regular hazard, cooling centers are typically opened in summer. Northern cities are also opening cooling centers as heat waves occur there more frequently than they did in the past. Urban areas with a lot of pavement and buildings – known as heat islands – can have temperatures well above the city’s average.

  • Hydrate, hydrate, hydrate! Drink plenty of fluids, and don’t forget about the importance of electrolytes. Heat-related dehydration can occur when people sweat excessively, losing water and necessary salts from the body. Some sports drinks or rehydration fluids restore electrolytes and hydration levels.

Older adults and people with disabilities often face higher risks from heat waves, particularly if they can’t easily move to a cooler environment. Communities and neighbors can help protect vulnerable populations by providing cooling centers and bottled water and making regular wellness checks during high heat.

Summer can be a season of fun. Just remember the risks, keep an eye on your friends and neighbors when temperatures rise, and plan ahead so you can beat the heat.The Conversation

Brian Bossak, Professor of Public Health, College of Charleston

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Note: The following A.I. based commentary is not part of the original article, reproduced above, but is offered in the hopes that it will promote greater media literacy and critical thinking, by making any potential bias more visible to the reader –Staff Editor.

Political Bias Rating: Centrist

This content provides practical, science-based information about heat-related health risks and safety tips without promoting any particular political ideology. It focuses on public health concerns, climate impacts on human health, and community measures to protect vulnerable populations in a neutral and informative way. The absence of partisan language or policy advocacy places it in the center of the political spectrum.

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50 years after ‘Jaws,’ researchers have retired the man-eater myth and revealed more about sharks’ amazing biology

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theconversation.com – Gareth J. Fraser, Associate Professor of Evolutionary Developmental Biology, University of Florida – 2025-06-18 10:06:00


The 1975 film *Jaws* sparked widespread fear of sharks, portraying them as ruthless killers. Limited scientific knowledge at the time allowed this myth to flourish. Yet the film also inspired a generation of researchers. Modern science has revealed sharks as complex, ancient creatures with unique adaptations—regenerative teeth, electroreception, biofluorescence, and global navigation skills. Despite their strength, sharks face modern threats from overfishing and habitat loss. Conservation efforts, including tagging and protections, have helped species like the great white rebound. Most sharks are harmless, misunderstood, and essential to ocean ecosystems—highlighting the need to replace fear with informed stewardship.

The shark in ‘Jaws’ became a terrifying icon.
Universal Pictures via Getty Images

Gareth J. Fraser, University of Florida

The summer of 1975 was the summer of “Jaws.”

movie poster for 'Jaws' with shark's toothy mouth under the water with a swimmer on the surface
The movie was adapted from a novel by Peter Benchley.
Universal History Archive/Universal Images Group via Getty Images

The first blockbuster movie sent waves of panic and awe through audiences. “Jaws” – the tale of a killer great white shark that terrorizes a coastal tourist town – captured people’s imaginations and simultaneously created a widespread fear of the water.

To call Steven Spielberg’s masterpiece a creature feature is trite. Because the shark isn’t shown for most of the movie – mechanical difficulties meant production didn’t have one ready to use until later in the filming process – suspense and fear build. The movie unlocked in viewers an innate fear of the unknown, encouraging the idea that monsters lurk beneath the ocean’s surface, even in the shallows.

And because in 1975 marine scientists knew far less than we do now about sharks and their world, it was easy for the myth of the rogue shark as a murderous eating machine to take hold, along with the assumption that all sharks must be bloodthirsty, mindless killers.

moviegoers lined up under the theater's marquee with 'JAWS' on it
People lined up to get scared by the murderous shark at the center of the ‘Jaws’ movie.
Bettmann Archive via Getty Images

But in addition to scaring many moviegoers that “it’s not safe to go in the water,” “Jaws” has over the years inspired generations of researchers, including me. The scientific curiosity sparked by this horror fish flick has helped reveal so much more about what lies beneath the waves than was known 50 years ago. My own research focuses on the secret lives of sharks, their evolution and development, and how people can benefit from the study of these enigmatic animals.

The business end of sharks: Their jaws and teeth

My own work has focused on perhaps the most terrifying aspect of these apex predators, the jaws and teeth. I study the development of shark teeth in embryos.

pinkish white fish embryo next to a larger yellowish sphere
Small-spotted catshark embryo (Scyliorhinus canicula), still attached to the yolk sac. This is the stage when the teeth begin developing.
Ella Nicklin, Fraser Lab, University of Florida

Sharks continue to make an unlimited supply of tooth replacements throughout life – it’s how they keep their bite constantly sharp.

Hard-shelled prey, such as mollusks and crustaceans, from sandy substrates can be more abrasive for teeth, requiring quicker replacement. Depending on the water temperature, the conveyor belt-like renewal of an entire row of teeth can take between nine and 70 days, for example, in nurse sharks, or much longer in larger sharks. In the great white, a full-row replacement can take an estimated 250 days. That’s still an advantage over humans – we never regrow damaged or worn-out adult teeth.

about a dozen rows of pointy teeth, all lined up
Magnified microscope image of a zebra shark (Stegostoma tigrinum) jaw. They have 20 to 30 rows of teeth in each jaw, each a new generation ready to move into position like on a conveyor belt. Humans have only two sets!
Gareth Fraser, University of Florida

Interestingly, shark teeth are much like our own, developing from equivalent cells, patterned by the same genes, creating the same hard tissues, enamel and dentin. Sharks could potentially teach researchers how to master the process of tooth renewal. It would be huge for dentistry if scientists could use sharks to figure out how to engineer a new generation of teeth for human patients.

Extraordinary fish with extraordinary biology

As a group, sharks and their cartilaginous fish relatives – including skates, rays and chimaeras – are evolutionary relics that have inhabited the Earth’s oceans for over 400 million years. They’ve been around since long before human beings and most of the other animals on our planet today hit the scene, even before dinosaurs emerged.

Sharks have a vast array of super powers that scientists have only recently discovered.

Their electroreceptive pores, located around the head and jaws, have amazing sensory capabilities, allowing sharks to detect weak electrical fields emitted from hidden prey.

looks like a face with a big eye and an open mouth, everything covered with little bumps
CT scan of the head of a small-spotted catshark (Scyliorhinus canicula) as it hatches. Skin denticles cover the surface, and colored rows of teeth are present on the jaws.
Ella Nicklin, Fraser Lab, University of Florida

Their skin is protected with an armor of tiny teeth, called dermal denticles, composed of sensitive dentin, that also allows for better drag-reducing hydrodynamics. Biologists and engineers are also using this “shark skin technology” to design hydrodynamic and aerodynamic solutions for future fuel-efficient vehicles.

green glowing sections on the front part of a fish against a black background
Fluorescent skin of the chain catshark (Scyliorhinus retifer).
Gareth Fraser, University of Florida

Some sharks are biofluorescent, meaning they emit light in different wavelengths after absorbing natural blue light. This emitted fluorescent color pattern suggests visual communication and recognition among members of the same species is possible in the dark depths.

Sharks can migrate across huge global distances. For example, a silky shark was recorded traveling 17,000 miles (over 27,000 kilometers) over a year and a half. Hammerhead sharks can even home in on the Earth’s magnetic field to help them navigate.

Greenland sharks exhibit a lengthy aging process and live for hundreds of years. Scientists estimated that one individual was 392 years old, give or take 120 years.

Still much about sharks remains mysterious. We know little about their breeding habits and locations of their nursery grounds. Conservation efforts are beginning to target the identification of shark nurseries as a way to manage and protect fragile populations.

Tagging programs and their “follow the shark” apps allow researchers to learn more about these animals’ lives and where they roam – highlighting the benefit of international collaboration and public engagement for conserving threatened shark populations.

Sharks under attack

Sharks are an incredible evolutionary success story. But they’re also vulnerable in the modern age of human-ocean interactions.

Sharks are an afterthought for the commercial fishing industry, but overfishing of other species can cause dramatic crashes in shark populations. Their late age of sexual maturity – as old as 15 to 20 years or more in larger species or potentially 150 years in Greenland sharks – along with slow growth, long gestation periods and complex social structures make shark populations fragile and less capable of quick recoveries.

Take the white shark (Carcharodon carcharias), for example – Jaws’ own species. Trophy hunting, trade in their body parts and commercial fishery impacts caused their numbers to dwindle. As a result, they received essential protections at the international level. In turn, their numbers have rebounded, especially around the United States, leading to a shift from critically endangered to vulnerable status worldwide. However, they remain critically endangered in Europe and the Mediterranean.

shark swims toward the camera with teeth visible in mouth, against blue ocean background
Protections and conservation measures have helped white sharks make a comeback.
Dave Fleetham/Design Pics Editorial/Universal Images Group via Getty Images

“Jaws” was filmed on the island of Martha’s Vineyard, in Massachusetts. After careful management and the designation of white sharks as a prohibited species in federal waters in 1997 and in Massachusetts in 2005, their populations have recovered well over recent years in response to more seals in the area and recovering fish stocks.

You might assume more sharks would mean more attacks, but that is not what we observe. Shark attacks have always been few and far between in Massachusetts and elsewhere, and they remain rare. It’s only a “Jaws”-perpetuated myth that sharks have a taste for humans. Sure, they might mistake a person for prey; for instance, surfers and swimmers can mimic the appearance of seals at the surface. Sharks in murky water might opportunistically take a test bite of what seem to be prey.

But these attacks are rare enough that people can shed their “Jaws”-driven irrational fears of sharks. Almost all sharks are timid, and the likelihood of an interaction – let alone a negative one – is incredibly rare. Importantly, there more than 500 species of sharks in the world’s oceans, each one a unique member of a particular ecosystem with a vital role. Sharks come in all shapes and sizes, and inhabit every ocean, both the shallow and deep-end ecosystems.

Most recorded human-shark interactions are awe-inspiring and not terrifying. Sharks don’t really care about people – at most they may be curious, but not hungry for human flesh. Whether or not “Jaws” fans have grown beyond the fear of movie monster sharks, we’re gonna need a bigger conservation effort to continue to protect these important ocean guardians.The Conversation

Gareth J. Fraser, Associate Professor of Evolutionary Developmental Biology, University of Florida

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Note: The following A.I. based commentary is not part of the original article, reproduced above, but is offered in the hopes that it will promote greater media literacy and critical thinking, by making any potential bias more visible to the reader –Staff Editor.

Political Bias Rating: Centrist

This content focuses on the biology, ecology, and conservation of sharks, presenting scientific information with references and without promoting a particular political ideology. It discusses environmental conservation in a factual and neutral manner, emphasizing the importance of protecting shark populations without attributing blame or engaging in politicized debates. The tone is educational and informative, reflecting a balanced perspective rooted in science rather than political bias.

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